Output intensity of light emitting diodes (LED's) is critical when they are used to provide timing marks during exposure of film, as in high speed photography. Light output of LED's varies and it is imperative that the light actually be within an acceptable range for proper film exposure. If the light output is too weak or too strong the exposure is unacceptable.
In film recording of important events that require time encoding, all of the data recorded has value which must be related to the start of the event. This is especially true, for example, in determining when a malfunction occured and what may have caused it. Thus, for example, at launches of a projectile where the launch and flight are being recorded at high speed, the film in addition to recording the event, also has projected onto one or both edges of the film timing light pulses which are captured by the film. If the light is too bright it will blur and not give an accurate reference center and can even affect the desired exposure of the event. If the light is too weak it will not record the timing. These situations result in wasted time, effort, film and there will be no data captured respecting the launched projectile.
In preliminary evalution of light emitting diodes used for providing timing pulses, testing procedures in use rely only on an observer viewing the diode to observe whether or not it appears to be reasonably bright. There are no actual measurements made of the light output. At present no measuring device indicating light output on timing LED's is readily available.